1. Field of the Invention
The present invention relates to a control device of a high-pressure fuel system of an internal combustion engine that includes fuel injection means (in-cylinder injector) for injecting a fuel into a cylinder at a high pressure, or an internal combustion engine that includes, in addition to the above fuel injection means, fuel injection means (intake manifold injector) for injecting a fuel into an intake manifold or an intake port. More particularly, the present invention relates to a technique for controlling a high-pressure fuel system having a plurality of high-pressure fuel pumps.
2. Description of the Background Art
An engine having a first fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine and a second fuel injection valve (intake manifold injector) for injecting a fuel into an intake manifold, and changing a fuel injection ratio between the in-cylinder injector and the intake manifold injector in accordance with the engine speed or the load of the internal combustion engine is known. A direct injection engine having only a fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine is also known. In a high-pressure fuel system including the in-cylinder injector, the fuel having its pressure increased by a high-pressure fuel pump is supplied via a delivery pipe to the in-cylinder injector, which injects the high-pressure fuel into a combustion chamber of each cylinder of the internal combustion engine.
Further, a diesel engine having a common rail fuel injection system is also known. In the common rail fuel injection system, the fuel having its pressure increased by a high-pressure fuel pump is stored in a common rail, and injected from the common rail into a combustion chamber of each cylinder of the diesel engine according to opening/closing of an electromagnetic valve.
To obtain the fuel of a high pressure in such internal combustion engines, a high-pressure fuel pump is used which has a cylinder driven by a cam provided at a driveshaft that is connected to a crankshaft of the internal combustion engine.
Japanese Patent Laying-Open No. 10-274075 discloses a cylinder injection internal combustion engine provided with cam-driven fuel pumps, which prevents variation in fuel amount among the cylinders due to discharge pulsation caused by the cam-driven fuel pumps. The cylinder injection internal combustion engine includes first and second cam-driven high-pressure fuel pumps that each perform suction and discharge of a fuel with a reciprocating motion of a plunger, slidably arranged in a pump housing, driven by a cam. The first high-pressure fuel pump is provided with a first discharge part that discharges the fuel at a first discharge timing. The second high-pressure fuel pump is provided with a second discharge part that discharges the fuel at a second discharge timing that has a desired phase difference Θ with respect to the first discharge-timing. Fuel injection valves include a first injection valve group that is branched on the downstream of the high-pressure fuel pumps and is supplied with the fuel at the first discharge timing, and a second injection valve group that is supplied with the fuel at the second discharge timing. With a pump speed reduction ratio represented by J and the number of cylinders of the engine represented by K, the number Y of cam crests at the cam part is set to satisfy Y×J=K/4, and phase difference Θ is set to satisfy Θ/J=720/K.
According to this cylinder injection internal combustion engine, the very simple configuration of providing two cam-driven high-pressure fuel pumps and setting the number of cam crests as well as the phase difference between the two high-pressure fuel pumps makes it possible to synchronize the pump pulsation cycles with the fuel injection cycles of the fuel injection valves, even in an engine having a large number of cylinders of which application is difficult. Accordingly, even in the event of large fluctuations of the fuel pressure due to the pump pulsation, the fuel injection pressure at the time of fuel injection becomes approximately equal among the cylinders, and the fuel of an approximately equal amount is injected from each cylinder. This also suppresses variation in air-fuel ratio among the cylinders.
Japanese Patent National Publication No. 2003-532833 discloses a fuel amount control system for an internal combustion engine having a particularly large combustion chamber or for an internal combustion engine having more than four cylinders, which ensures highly reliable fuel supply to a combustion chamber. The fuel amount control system includes a fuel reserve tank, at least one pre-feed pump, a high-pressure fuel pump device provided with at least two high-pressure fuel pumps for delivering a fuel from a low-pressure area to at least one high-pressure accumulator, a control device for controlling an injection pressure formed within the high-pressure accumulator, and a plurality of fuel injection valves for injecting the fuel from the high-pressure accumulator into a plurality of combustion chambers of the internal combustion engine. The fuel amount control system has a single fuel circuit for controlling the amounts of the fuel to be supplied to the combustion chambers of the internal combustion engine. The high-pressure fuel pumps are all arranged in this fuel circuit, and the fuel circuit controls the high-pressure fuel pumps independently from each other using a single pressure control circuit commonly provided.
In this fuel amount control system, only one fuel circuit, rather than a plurality of fuel circuits, is provided for controlling the amounts of the fuel supplied to every combustion chambers of the internal combustion engine, and the high-pressure fuel pumps of the high-pressure fuel pump device are all arranged in this fuel circuit. The control device of the fuel amount control system controls the high-pressure fuel pumps independently from each other via one common pressure control circuit. There is only one high-pressure accumulator arranged in the fuel circuit. The injection pressure of this high-pressure accumulator can be controlled with the single pressure control circuit. As such, a fuel amount control system ensuring highly reliable fuel supply to the combustion chambers can be implemented inexpensively with a particularly simple configuration.
However, although Japanese Patent Laying-Open No. 10-274075 and Japanese Patent National Publication No. 2003-532833 both disclose configuration of a high-pressure fuel system with a plurality of (two) high-pressure fuel pumps, they fail to disclose how to control the plurality of high-pressure fuel pumps in a cooperative manner so as to obtain a desired discharge pressure.